This invention relates to joysticks, and in particular to optical joysticks.
Joysticks are used for a variety of purposes in a variety of different circumstances. For example they are used in computer systems to control the position of a pointer on a screen, as well as being used in a variety of vehicles (such as a helicopter for example) to control the direction of motion of the vehicle.
Whilst a variety of different types of joystick have previously been proposed, they all share a number of common features. For example, all joysticks have a shaft which can be gripped at one end by a user and pivoted about a fixed point in (at least) a two dimensional (X and Y) space. Coupled to the other end of the shaft is some sort of control system which is operable to convert movement of the shaft in the space into electrical signals.
The earliest joysticks were mechanical joysticks, so called because they used a part-mechanical control system to convert movement of the shaft into electrical signals. FIG. 1 is a cross-sectional view through the base of one such mechanical joystick. As shown, the joystick 1 includes a pair of potentiometers 10, 12 which are mounted on a common frame 14. A shaft 16 is provided, and one end of the shaft is coupled to a stationary member (such as the floor of the joystick) by a universal joint so that the other end of the shaft 16 can move in both X and Y directions. The control shafts of the potentiometers 10 and 12 are coupled to the shaft 16 by respective arm members 18 and 20 which each include an elongated opening 22, 24.
As the shaft is moved in the X direction it bears against the arm member 20 (without bearing on the other arm 18) and causes it to tilt about its axis. As the arm 20 tilts it rotates the control shaft of the potentiometer 12, and so varies the resistance of that potentiometer. The change in resistance of the potentiometer 12 is directly proportional to the extent to which the control shaft is rotated and thus provides an accurate means to measure the amount of shaft deflection in the X direction.
In a similar fashion, if the shaft is moved in the Y direction it bears against the arm member 18 (without bearing on the arm 20) and causes it to tilt about its axis to vary the resistance of the potentiometer 10 connected thereto.
As will be apparent from FIG. 1, if the joystick is moved in directions other than along the X or Y axes, then both potentiometers 10 and 12 will be rotated simultaneously and the exact position of the shaft in the space can be read out based on the relative resistances of the two potentiometers.
A problem with this previously proposed joystick is that as the potentiometers are mechanical devices, they are subject to wear and as a result will eventually fail. When this happens the potentiometers must be replaced if the user wishes to avoid having to purchase a new joystick. Another problem is that the greased control shafts of the potentiometers tend to attract fluff and other detritus which can impair smooth rotation of the control shafts.
To alleviate these problems it has previously been proposed, in United Kingdom Patent Application No. 2334573 for example, to use optical components which are free from the problems which typically face corresponding mechanical components.
FIG. 2 illustrates the joystick described in UK Patent Application No. 2334573. As shown, the shaft 2, 5 of the joystick 1 includes an optical emitter 3 which is adapted to illuminate a bank of optical detectors 9, 10, 11, 12 arranged on the floor of the joystick. As the shaft is moved about the two-dimensional space the emitter illuminates each of the detectors to a different degree, and hence the quantity of light detected by each of the detectors 9, 10, 11 and 12 varies. As the quantity (or intensity) of detected light varies the electrical signals output from the detectors also vary. Control electronics (not shown) interpret the signals output from the detectors to compute the position of the shaft in the space.
Whilst the joystick of FIG. 2 avoids the problems associated with the joystick of FIG. 1, it has its own set of disadvantages.
A first of these is associated with the fact that each of the detectors tend to detect an amount of light which can vary only to a small extent from that received by neighbouring detectors. As a result of this, the control electronics need to be quite sophisticated and carefully designed to enable position information to be accurately determined.
A further problem with the joystick of FIG. 2, and indeed with that of FIG. 1, is that it is not easy to adapt the joystick to provide anything other than a linear response between shaft movement and signal output. One might want to do this, for example, if the joystick is to be used in a computer system for handicapped or otherwise disabled users where it would be useful for the joystick to have a response where the effect of involuntary hand movements (such as a tremor for example) on cursor movement is reduced. Similarly, a non-linear response would assist those persons who only have a relatively poor amount of movement to control the position of a cursor on a screen.
U.S. Pat. No. 4,533,827 discloses another optical joystick which alleviates the first mentioned problem associated with the joystick of FIG. 2. As shown in FIG. 3, the joystick proposed in this U.S. patent employs a number of emitter/detector pairs 20-26 spaced about the periphery of a central sphere 18. The outside surface of the sphere is painted so that it varies smoothly from being wholly reflective (for example at the top of the sphere) to being wholly non-reflective (for example at the bottom of the sphere). As the joystick of FIG. 3 is moved, the sphere moves with it, and the quantity of light detected by each of the detectors varies accordingly. Since the emitter/detector pairs of the joystick of FIG. 3 are separated from one another, it is unlikely that illumination from any one emitter will have any real effect upon any other detector outside of its emitter/detector pair.
However, a major disadvantage of the joystick shown in FIG. 3 is that as the sphere goes from reflective to non-reflective in front of one emitter/detector pair, it will tend to go from non-reflective to reflective in front of the other emitter/detector pair. This disadvantage is exacerbated if the reflectivity of the sphere varies non-linearly.
The only way to avoid this disadvantage of the joystick shown in FIG. 3 is to adapt the control electronics so that one emitter/detector pair output is inverse to that of the other. This complicates the control electronics of the joystick, and hence increases the cost of the joystick.
The present invention has been conceived with the aim of alleviating the above-described problems.
In pursuit of this aim, one embodiment of the invention provides a joystick comprising: a control shaft; first and second reflecting surfaces, said surfaces each having a reflectivity that varies along a notional line on said surface; a first sensor assembly comprising a first emitter operable to illuminate said first reflecting surface along said line with radiation, and a first detector arranged to detect radiation emitted by said first emitter and reflected by said first reflecting surface; and a second sensor assembly comprising a second emitter operable to illuminate said second reflecting surface along said line with radiation, and a second detector arranged to detect radiation emitted by said second emitter and reflected by said second reflecting surface; wherein movement of said shaft provides a relative movement between emitters of the first and/or second sensor assemblies and respective associated reflecting surfaces to vary the intensity of radiation reflected, and said detectors of said first and second sensor assemblies are each operable to output a voltage that is dependent on the intensity of radiation detected.
The joystick of this embodiment is advantageous over joysticks of the type shown in FIG. 1 because of the fact that the optical movement detection system is free from the problems that are characteristic of prior art mechanical joysticks. Furthermore, as the detector/emitter pairs are well spaced from one another so the likelihood of light from one emitter being detected by the detector of the other emitter/detector pair is significantly reduced, and thus the joystick of this embodiment is advantageous over the joystick of FIG. 2.
The joystick of this embodiment is also advantageous over the joystick shown in FIG. 3 because of the fact that the control electronics do not need to be designed to compensate for outputs which vary in the opposite sense from one another. Unusually (and indeed contrary to normal expectations in the art) the joystick of this embodiment also provides advantages which result from the fact that it is more complicated than prior art optical joysticks of the type shown in FIG. 3. In particular, by increasing the number of reflecting surfaces it is possible to more easily provide different non-linear reflectivity variations. This is something that one might realistically want to do in circumstances where the user of the joystick is physically impaired only in one direction of movement.
In accordance with a further embodiment of the invention, there is provided a joystick comprising: a control shaft moveable throughout a two dimensional space defined by X and Y axes; first and second reflectors each having a surface with a reflectivity that varies along one axis of the reflector; a first sensor assembly comprising a first emitter operable to illuminate portions of said first reflector surface with a beam of radiation, and a first detector arranged to detect radiation emitted by said first emitter and reflected by said first reflector surface; a second sensor assembly comprising a second emitter operable to illuminate portions of said second reflector surface with a beam of radiation, and a second detector arranged to detect radiation emitted by said second emitter and reflected by said second reflector surface; and means for transforming movement of the shaft into relative movement between emitters of the first and/or second sensor assemblies and respective associated reflectors; wherein said transform means is operable: on movement of said shaft along said X axis to establish a relative movement which causes said beam of said first emitter to track generally along said first reflector axis; on movement of said shaft along said Y axis to establish a relative movement which causes said beam of said second emitter to track generally along said second reflector axis; and on any other movement of said shaft to establish a relative movement which causes said beam of said first and second emitters to track generally along said first and second reflector axes, respectively.
Other advantages of embodiments of the invention will be apparent once the following description has been read and understood.